The conversion of hydrocarbons to hydrogen and carbon monoxide containing gases is well known in the art. Examples of such processes include catalytic steam reforming, auto-thermal catalytic reforming, catalytic partial oxidation and non-catalytic partial oxidation. Each of these processes has advantages and disadvantages and produces various ratios of hydrogen and carbon monoxide, also known as synthesis gas. The present invention is directed to a hydrocarbon cracking process for producing hydrogen or a methane-hydrogen mixture through the use of a monolith based catalyst. The present invention is also directed towards the production of synthesis gas from a single unit reactor.
Partial oxidation processes are also well known and the art is replete with various catalytic partial oxidation processes. Partial oxidation is an exothermic reaction wherein a hydrocarbon gas, such as methane, and an oxygen-containing gas, such as air, is contacted with a catalyst at elevated temperatures to produce a reaction product containing high concentrations of hydrogen and carbon monoxide. The catalysts used in these processes are typically noble metals, such as platinum or rhodium, and other transition metals, such as nickel on a suitable support.
Partial oxidation processes convert hydrocarbon-containing gases, such as natural gas, to hydrogen, carbon monoxide and other trace components such as carbon dioxide and water. The process is typically carried out by injecting preheated hydrocarbons and an oxygen-containing gas into a combustion chamber where oxidation of the hydrocarbons occurs with less than stoichiometric amounts of oxygen for incomplete combustion. This reaction is conducted at very high temperatures, such as in excess of 700° C. and often in excess of 1,000° C., and pressures up to 150 atmospheres. In some reactions, steam or carbon dioxide can also be injected into the combustion chamber to modify the synthesis gas product and to adjust the ratio of hydrogen to carbon monoxide.
More recently, partial oxidation processes have been disclosed in which the hydrocarbon gas is contacted with the oxygen-containing gas at high space velocities in the presence of a catalyst such as a metal deposited on a ceramic foam (monolith) support. The monolith supports are impregnated with a noble metal such as platinum, palladium or rhodium, or other transition metals such as nickel, cobalt, chromium and the like. Typically, these monolith supports are prepared from solid refractory or ceramic materials such as alumina, zirconia, magnesia and the like. During operation of these reactions, the hydrocarbon feed gases and oxygen-containing gases are initially contacted with the metal catalyst at temperatures in excess of 400° C., typically in excess of 600° C., and at a standard gas hourly space velocity (GHSV) of over 100,000 per hour.
However, these processes still require downstream separation to obtain hydrogen and/or carbon monoxide as separate products. In the hydrocarbon cracking process of this invention, hydrogen and carbon monoxide are separately produced directly in a single reactor by operating in a cyclic fashion.
Earlier methods for producing hydrogen from hydrocarbon decomposition suffer from excessive pressure drop in fixed bed operations or operational complexity in circulating fluid beds. The present method will provide a solution to these problems as the ceramic monolith has a high porosity with large pore size and will cause negligible pressure drop during operation. Further, there is no movement of the catalyst and the resulting attrition, plugging or other problems associated with circulating fluid beds. In addition, earlier methods focused upon the products being either only hydrogen (M. Poirier and C. Sapundzhiev) or hydrogen and carbon products (N. Muradov). The present method will enable the generation of pure CO selectively over CO2 by tuning the operation parameters of regeneration oxygen containing stream and CO can be collected continuously; thus upgrading the value of products significantly.